The present invention relates to a fuel adjustment and filtering device for a high-pressure pump in an injection system for an internal combustion engine.
As it is known, fuel injection systems of internal combustion engines typically comprise a low-pressure fuel pump to take the fuel from the usual tank and send it to the high-pressure pump. This sends the pressurised fuel to a common rail connected to the various engine cylinder injectors. The system further comprises a fuel filter and devices for controlling the rail fuel pressure.
Injection systems are known wherein the high-pressure pump is of the variable flow rate type, and is controlled to avoid pumping excess fuel in respect to what is required by the injectors, thus reducing the work performed by the high-pressure pump and therefore increasing the engine efficiency. In a known system, the high-pressure pump flow rate is metered by a shut-off solenoid valve, arranged on the intake pipe of the pump and controlled by a control unit, according to the operative conditions of the engine.
It has also been proposed to insert, in the intake pipe of the high-pressure pump, a control valve adapted to adjust the pressure of the fuel, upstream of the shut-off solenoid valve, to a predetermined value. This valve sends the excess fuel received from the low-pressure pump, to the high-pressure pump, from where it is discharged into the fuel tank. The excess fuel lubricates and cools the operating mechanism of such pump before returning to the tank. Furthermore, in order to avoid load losses and hydraulic resonance waves between the two pumps, the shut-off solenoid valve and the pressure control valve of the fuel to intake must be reciprocally arranged as close as possible.
In the high-pressure pumps of the known art, in general the fuel filter is arranged between the low-pressure pump and the high-pressure pump. Furthermore, the shut-off solenoid valve and the pressure control valve are integrated with the high-pressure pump and are accommodated in a common casing, which comprises the high-pressure crankcase, thus forming the pump body in which the various pumping elements are housed. Such an integration however creates a considerable complexity in the hydraulic connection of the adjustment valve and of the shut-off valve. The pump body therefore appears relatively heavy and cumbersome, thus requiring a complicated and costly manufacture.
For automobile engines, in which the injection system must be assembled within the usual engine housing, it also appears difficult to find space for such high-pressure pump near the usual common rail on the engine head. Finally, as it is known, the shut-off solenoid valve comprises some delicate electrical components, some plastic electrical connectors, and some other parts more fragile than the pump body, which is generally formed by cast iron. The solenoid valve can be subjected to damage both during assembly on the engine and in the case of automobile collisions or accidents, endangering its operation. In the case of automobile accident, a dangerous leakage of fuel may further be generated.
The present invention relates to providing a fuel adjustment and filtering device for a high-pressure pump of an injection system, which is easy to manufacture and to assemble and of low cost, eliminating the drawbacks of the devices of the known art.